GitLab/Repo: Enable/Add sequence diagram

The steps are:

• Enable PlantUml in GitLab: 
  • Login to GitLab -> Admin Area -> Settings -> Scroll down to PlantUML
  • Enable PlantUML
  • In PlantUML URL: type “https://www.plantuml.com/plantuml” and save changes

• Use Planttext as the online PlantUML editor to build/test your diagram
• Use http://plantuml.com/ as reference for example code and documentation
• Go to your repository
• Add “Readme.md” file and click edit
• Add the code below:

```plantuml
@startuml  
skinparam backgroundColor #EEEBDC 
skinparam ParticipantPadding 50 

Title: Application overview actor user order 10 
participant "Front end - Angular" order 20 
participant "Back end - .Net Core API" order 30 
database db order 40 

user-->"Front end - Angular": Login to site  
||20|| 
"Front end - Angular"-[#red]->"Back end - .Net Core API": Request message 
||40|| 
activate "Back end - .Net Core API" 
"Back end - .Net Core API"-[#blue]->db: Data fetch\n from db 
activate db 
db-[#blue]->"Back end - .Net Core API": Data fetch\n from db 
||40|| 
deactivate db 
"Back end - .Net Core API"-[#red]->"Front end - Angular": Response message 
||40|| 
deactivate "Back end - .Net Core API" 
"Front end - Angular"-->user: Done 
@enduml 
```

Edit:

Preview: